Extrusion molding apparatus and an apparatus for controlling the same

ABSTRACT

This invention aims to shorten cycle time by allowing a robot to be operated with speed capability regardless of the shape of moldings. An extrusion molding apparatus has an extrusion molding machine which delivers an extrusion material which becomes a frame-shaped molding through a nozzle fore end, and a robot which holds a workpiece on which the molding is formed and whose working speed is set so as to make travel speed of workpiece rectilinear portions with respect to the nozzle fore end higher than travel speed of workpiece corner portions with respect to the nozzle fore end. Thus, changes in workpiece travel speed with respect to the nozzle fore end are allowed, and robot working speed is not restricted by the shape of moldings.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an extrusion molding apparatus for formingframe-shaped moldings integrally on the periphery of a panel such as anautomobile windowpane, or producing moldings as independent componentparts, and to a control apparatus of an extrusion molding apparatuswhich is capable of controlling the cross-sectional shape of moldingsproduced by the aforesaid extrusion molding apparatus with highprecision.

2. Description of the Related Art

As is often the case, a frame-shaped molding 1 is integrally formed onthe periphery of a panel such as an automobile windowpane, as shown inFIGS. 17(A) and 17(B). (Refer to Japanese Unexamined Patent Publication(KOKAI) No. 4-261822.) For formation of the above molding 1, employed isa cooperation system of an extrusion molding machine which discharges anextrusion material as a molding 1 from a nozzle fore end 4, and a robotwhich holds an automotive windowpane 2 (hereinafter referred to as aworkpiece) and enables the workpiece 2 to make complex motion ofrectilinear motion and rotary motion with respect to the above nozzlefore end 4. The extrusion molding machine delivers an extrusion materialsuch as molten resin and discharge the material continuously from thenozzle fore end 4 by such a rotary actuator as a motor (hereinafterreferred to as a molding machine actuator). The extrusion moldingmachine is located in such a manner that the peripheral portion of aworkpiece making the above complex motion moves across the nozzle foreend 4. The nozzle fore end 4 is provided with a mouthpiece for renderinga cross sectional shape of the molding 1 to the extrusion material, asdiscussed later.

Therefore, when the robot is operated at a certain speed, a workpiece 2is transferred with respect to the nozzle fore end 4, and such a molding1 as shown in FIGS. 17(A) and 17(B) is integrally formed on theperiphery of the workpiece. It will be appreciated that the peripheralportion of a workpiece is coated with primer 5, which will be formedinto an adhesive layer by heat and pressure of the extrusion material.

In this type of extrusion molding, to obtain precise cross-sectionalshape of moldings continuously, it is a fundamental technique tomaintain a discharged amount of an extrusion material per unit time fromthe nozzle fore end constant, and workpiece travel speed, i.e.,workpiece peripheral speed V constant.

In this case, in order to keep workpiece peripheral speed V constant,robot working speed V_(A) at the time when workpiece peripheral speed atworkpiece rectilinear portions is V is limited by robot working speed atthe time when workpiece peripheral speed at workpiece corner portions isV. Consequently, there arises a drawback in which time for forming amolding on a workpiece (hereinafter referred to as cycle time) islengthened.

In other words, in order to make peripheral speed V of workpiece cornerportions equal to peripheral speed V of workpiece rectilinear portions,working speed V_(A) of the robot in transferring the workpiecerectilinear portions must be lower than working speed V_(B) of the robotin transferring the workpiece corner portions. As a result, cycle timeis determined by workpiece peripheral travel distance (mm)/travel speedof workpiece corner portions (mm/sec). This is longer than designedcycle time on the base of robot speed capability. Therefore, it isdifficult to meet the demand for mass production fully.

In this regard, in order to reduce cycle time by decreasing time fortranferring rectilinear portions, it can be thought of to changeperipheral speed V of workpiece rectilinear portions from that ofworkpiece corner portions, and at the same time, control working speedof an extrusion molding machine actuator (e.g., screw rotational speed)in such a manner that the discharged amount of an extrusion material isrelatively changed to follow up changes in peripheral speed V.

The discharged amount of an extrusion material from the nozzle fore end,however, is a physical quantity which is dependent on the pressure ofextruding an extrusion material by the molding machine actuator. Aregression formula which expresses the relation between working speed ofthe molding machine actuator and the pressure of extruding an extrusionmaterial from the nozzle fore end (hereinafter referred to simply asmaterial extruding pressure) has a nonlinear difference factor and atime difference factor.

Therefore, when general feedback control based on proportional,integral, and derivative (PID) action is exercised to allow the materialextruding pressure to follow up changes in working speed of the moldingmachine actuator, it takes a long time to set a regression formula andexamine whether it is correct or not. Besides, since the above generalcontrol involves no steps of storing the above time difference factorand correcting data by the factor in advance, the delay in controlbecomes so remarkable that precise cross-sectional shape of moldingscannot be maintained.

In addition, the material extruding pressure is liable to have a gapwith a target value because of disturbance such as outside airtemperature, and this makes automatic control in continuous productiondifficult.

SUMMARY OF THE INVENTION

The present invention has been conceived to overcome the above problems.

It is an object of the present invention to reduce cycle time byallowing a robot to be operated with speed capability regardless of theshape of moldings.

It is a further object of the present invention to reduce variations inthe cross-sectional shape of moldings even when workpiece travel speedchanges, and at the same time facilitate preparatory work before moldingsuch as setting of a regression formula.

To achieve the foregoing objects, the present invention has allowedworkpiece travel speed with respect to a nozzle fore end to be changedso that robot working speed is not restricted by the shape of moldings.

An extrusion molding apparatus according to a first aspect of thepresent invention comprises an extrusion molding machine having amolding machine actuator which delivers an extrusion material whichbecomes a frame-shaped molding through a nozzle fore end, and

a robot which holds a workpiece on which the molding is formed whilehaving the workpiece make complex motion of rectilinear motion androtary motion, and whose working speed is set so as to make travel speedof workpiece rectilinear portions with respect to the nozzle fore endhigher than travel speed of workpiece corner portions with respect tothe nozzle fore end which is restricted by the distance between thecorner portions of the above molding and the center of the rotarymotion.

According to a second aspect of the present invention, a controlapparatus which controls the actuator of the aforementioned extrusionmolding machine comprises speed data input means, difference factorcalculating means, and operating means, and is realized mainly by acontroller with a general CPU. The speed data input means is constitutedby RAM or a register accessed by the CPU. The difference factorcalculating means is composed of ROM or RAM on which it is possible towrite one regression formula expressing the relation of any two of theworkpiece travel speed, material extruding pressure at the nozzle foreend, and working speed of the molding machine actuator, and ALU whichcalculates at least one of a nonlinear difference factor and a timedifference factor between material extruding pressure and working speedof the above molding machine actuator on the base of the workpiecetravel speed, in cooperation with the ROM or RAM. The operating meansincludes an electric power output circuit for driving the above moldingmachine actuator, and can be constituted by an electric circuit whichgenerates control signals to output driving signals to the moldingmachine actuator, and supplies those signals to the electric poweroutput circuit.

According to the third aspect of the present invention, the controlapparatus uses a regression formula expressing the relation between theworkpiece travel speed and material extrusion pressure at the abovenozzle fore end. The control apparatus is provided with pressuredetecting means for detecting material extruding pressure at the nozzlefore end, and calculates difference, as a nonlinear difference factor,between pressure detected by the pressure detecting means and materialextruding pressure calculated by using the regression formula.

According to a fourth aspect of the present invention, the controlapparatus produces time series points when workpiece travel speedchanges, and working speed instruction values (basic data) for themolding machine actuator which are required at the respective timeseries points, by the basic data production means. In addition, thecontrol apparatus reads the waveform of workpiece travel speed for onecycle, and calculates a time difference factor between materialextruding pressure and working speed of the above molding machineactuator at each of the above time series points, on the base ofworkpiece speed change rate obtained by differentiating the waveform ofworkpiece travel speed, and the workpiece travel speed. Then, on thebase of the above time difference factor, the control apparatus shiftsthe basic data along the time axis in advance of each of the time seriespoints when the workpiece travel speed changes.

According to a fifth aspect of the present invention also concerns acontrol apparatus for controlling the actuator of the above extrusionmolding machine. This control apparatus reads workpiece travel speed forone cycle beforehand, sets basic data at the time series points when thechange rate of this workpiece travel speed varies. Then, during theextrusion molding based on the above basic data, the control apparatuscalculates time difference between the time series points when pressurechange rate obtained from the waveform of detected pressure for onecycle, and the time series points based on the above workpiece travelspeed, corrects the above basic data by the time difference and switchesthem with corrected data in sequence.

The nonlinear difference factor is difference between the characteristicof variations in workpiece travel speed and the characteristic ofvariations in material extruding pressure.

It should be noted that the present invention according to the second tofifth aspects of the invention can be carried out, for example, bydisplaying a graph which indicates points of change in workpiece travelspeed on a screen, and achieving molding with manual operation forchanging working speed of the molding machine actuator before thesepoints of change.

Now, the operation of the present invention is as follows.

According to the first aspect of the present invention, in the casewhere a molding is formed on the periphery of a workpiece, even when theworkpiece travel speed, i.e., workpiece peripheral speed is lowered atcorner portions, there is no need to reduce the workpiece peripheralspeed at rectilinear portions in conformity with that low speed. Therobot can be operated with speed capability.

According to the second aspect of the present invention, the controlapparatus reads workpiece peripheral speed before molding, andcalculates a nonlinear difference factor or a time difference factorbetween the waveform of workpiece peripheral speed and the waveform ofmaterial extruding pressure. Then, on the base of this differencefactor, the control apparatus corrects control signals for instructingworking speed of the molding machine actuator in advance of changes inworkpiece peripheral speed.

According to the third aspect of the present invention, since thecontrol apparatus reads workpiece peripheral speed before molding, andcalculates a nonlinear difference factor between the waveform ofworkpiece travel speed and the waveform of material extruding pressure,it is possible to prevent variations in cross-sectional shape attributedto the nonlinear difference factor.

According to the fourth aspect of the present invention, the controlapparatus sets basic data for instructing working speed of the moldingmachine actuator at time series points when workpiece travel speedchanges. Then, the control apparatus calculates a time difference factorbetween material extruding pressure and working speed of the moldingmachine actuator at the above time series points, on the base ofworkpiece travel speed, and workpiece speed change rate obtained bydifferentiating the workpiece travel speed. On the base of the obtainedtime difference factor, the control apparatus shifts the above basicdata along the time axis in advance of the above time series points whenthe above workpiece travel speed changes, and outputs corrected basicdata to the operating means. Thus, the control apparatus can attaincontrol in which changes in workpiece travel speed are read beforehandand material extruding pressure is controlled to follow up the changesin workpiece travel speed.

According to the fifth aspect of the present invention, the controlapparatus calculates time difference between the time series points whenworkpiece peripheral speed changes and the time series points whenmaterial extruding pressure changes in every cycle. Based on the timedifference, the control apparatus calculates advanced time series pointsfor outputting control signals for instructing working speed of themolding machine actuator with respect to the time series points whenworkpiece peripheral speed changes. Besides, the control apparatuscorrects the former control signals to control signals which arenecessary at the advanced time series points.

Now, advantages of the present invention will be discussed.

According to the first aspect of the present invention, even whenworkpiece travel speed is lowered at the corner portions, there is noneed to lower workpiece travel speed at the rectilinear portions inconformity with that low speed. Thus, the robot can be operated withspeed capability, and cycle time can be reduced considerably.

According to the second aspect of the present invention, working speedof the molding machine actuator can be controlled so that materialextruding pressure always follows up workpiece travel speed. Therefore,even when workpiece travel speed at the corner portions is differentfrom workpiece travel speed at the rectilinear portions, an effect ofsuppressing variations in cross-sectional shape by the essentialtechnique can be maintained.

In addition, because the regression formula used herein is a simplelinear expression, a coefficient can be easily set with a slightmodification in view of disturbance.

According to the third aspect of the present invention, it is possibleto prevent variations in cross-sectional shape attributed to a nonlineardifference factor between the waveform of workpiece travel speed and thewaveform of material extruding pressure.

According to the fourth aspect of the present invention, it is possibleto prevent variations in cross-sectional shape attributed to a timedifference factor between material extruding pressure and working speedof the molding machine actuator.

According to the fifth aspect of the present invention, control signalsfor the molding machine actuator can be corrected in every cycle ofmolding. Therefore, variations in the cross-sectional shape of moldingscan be reduced even when there are disturbance such as changes intemperature environment, and variation in resin material characteristicvalues.

BRIEF DESCRIPTION OF THE DRAWINGS

The exact nature of this invention, as well as other objects andadvantages thereof, will be readily apparent from consideration of thefollowing specification relating to the annexed drawings in which:

FIG. 1 is a perspective view of an extrusion molding apparatus accordingto the present invention;

FIG. 2 is an exploded view of a nozzle fore end of an extrusion moldingmachine according to the present invention;

FIGS. 3(A) and 3(B) are drawings for explaining workpiece movementsaccording to the present invention, and FIG. 3(A) shows workpiecerectilinear motion and FIG. 3(B) shows workpiece movements at a cornerportion;

FIG. 4(A) shows the waveform of workpiece travel speed, and FIG. 4(B)shows the waveform of material extruding pressure, with regard to theextrusion molding machine according to the present invention;

FIG. 5 is a block diagram of a control apparatus of an extrusion moldingapparatus of a first preferred embodiment of the present invention;

FIG. 6 is a graph showing a regression formula used in the firstpreferred embodiment of the present invention;

FIG. 7 is a flow chart showing programs carried out by the controlapparatus of the first preferred embodiment of the present invention;

FIG. 8 is a block diagram of a control apparatus of an extrusion moldingapparatus of a second preferred embodiment of the present invention;

FIG. 9 is a flow chart showing the programs carried out by the controlapparatus of the second preferred embodiment of the present invention;

FIGS. 10(A), 10(B) and 10(B) are time charts for the control apparatusof the second preferred embodiment of the present invention, and FIG.10(A) shows the waveform of workpiece travel speed, FIG. 10(B) shows thewaveform of material extruding pressure, and FIG. 10(C) shows thewaveform of control signals for the molding machine actuator;

FIG. 11 is a graph showing a regression formula set in the secondpreferred embodiment;

FIG. 12 is a block diagram of a control apparatus of a third preferredembodiment of the present invention;

FIG. 13 is a flow chart showing programs carried out by the controlapparatus of the third preferred embodiment of the present invention;

FIG. 14 is a graph showing a regression formula set in the thirdpreferred embodiment of the present invention;

FIGS. 15(A), 15(B), and 15(C) are time charts for explaining programscarried out by the control apparatus of the third preferred embodimentof the present invention, and FIG. 15(A) shows the waveform of workpiecetravel speed, FIG. 15(B) shows the waveform of workpiece speed changerate obtained by differentiating the waveform of the workpiece travelspeed, and FIG. 15(C) shows the waveform of basic data;

FIGS. 16(A), 16(B), 16(C), and 16(D) are also timing charts forexplaining the programs carried out by the control apparatus of thethird preferred embodiment of the present invention, and FIG. 16(A)shows the waveform of detected pressure, FIG. 16(B) shows the waveformof pressure change rate obtained by differentiating the waveform of thedetected pressure, and FIG. 16(C) shows a time chart showing therelation between the time series points about workpiece travel speed andthe time series points about detected pressure, and FIG. 16(D) shows thewaveform of corrected basic data;

FIGS. 17(A) is a perspective view of a molding formed on a panel andproduced by the present invention and FIG. 17(B) is a cross-sectionalview taken along line II--II of FIG. 17(A); and

FIGS. 18(A) and 18(B) are drawings for explaining workpiece movements ina conventional extrusion molding apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be discussed in detail by way ofpreferred embodiments.

Basic Construction

FIG. 1 shows an extrusion molding apparatus according to the presentinvention.

In FIG. 1, a robot 11 has an arm 12 which has a wide freedom and whoseoperation is instructed by a robot control panel 14. An attachment 13for holding a workpiece 2 is fixed to a fore end of the arm 12. Theworkpiece 2 is held by the attachment 13 in such a way that a holdingcenter 3 makes complex motion of rectilinear motion and rotary motion,as shown in FIGS. 3(A) and 3(B).

An extrusion molding machine 15 has a construction in which an extrusionmaterial which has been supplied to a hopper 16 is delivered to a nozzlefore end 4 and discharged from the nozzle fore end 4 by a motor 10, andto the motor 10 control signals 20 are supplied from a molding machinecontrol panel 17 by way of communication cable 18. These control signals20 are to instruct rotational speed N of the motor 10 according to thepresent invention.

On the other hand, speed instruction signals 21 for instructingworkpiece travel speed, i.e., workpiece peripheral speed V istransferred from the aforementioned robot control panel 14 to themolding machine control panel 17 by way of communication cable 19.

As shown in FIG. 2, the nozzle fore end 4 has a slit 4a which is to beengaged with a peripheral portion of a workpiece 2. A mouthpiece 22having a discharge port 22a which communicates with the slit 4a isattached to the nozzle fore end 4. The discharge port 22a restricts thecross-sectional shape of an extrusion material.

In first and third preferred embodiments as mentioned later, a pressuresensor 23 is provided at the nozzle fore end 4 to achieve control withdetection of material extruding pressure at the discharge port 22a. Inthese preferred embodiments, pressure data P_(d) detected by thepressure sensor 23 are transferred to the molding machine control panel17 by way of communication cable 24.

The pressure sensor 23 may be installed, for example, by providing asemiconductor film for detecting mechanical distortion, on the nozzlefore end 4 directly, or by dividing a constant pressure chamber withsuch a semiconductor film.

The feature of the above extrusion molding apparatus resides in that theentire periphery of a workpiece is not transferred at constant speedwhich is restricted by the workpiece peripheral speed at the workpiececorner portions, and in that robot working speed is controlled so thatthe workpiece peripheral speed at workpiece rectilinear portions aloneattains a high speed. In other words, in contrast to the prior art shownin FIGS. 18(A) and 18(B), robot working speed V_(A) in moldingrectilinear portions which do not require a decrease in speed is notrestricted by robot working speed V_(B) in molding corner portions whichrequire a decrease in workpiece travel speed in accordance with thedistance between the holding center 3 and the corner portions, so as toinhibit constant workpiece peripheral speed on the entire periphery ofthe workpiece. As apparent from a comparison of FIG. 3(A) with FIG.18(A), robot working speed V_(A) ' in molding workpiece rectilinearportions is set to satisfy V_(A) '>V_(A), in order that V₁ >V₂.

Therefore, as shown in FIG. 4(A), a workpiece 2 travels at a high speedV₁ in rectilinear travel sections L_(A) with respect to the nozzle foreend 4, and at a low speed V₂ in corner travel sections L_(B).

In order to adopt the aforementioned fundamental technique to aworkpiece which is traveled at a higher workpiece peripheral speed inrectilinear sections as mentioned above, the present invention needs tocontrol a discharging amount (flow rate) of an extrusion material inresponse to variations in workpiece peripheral travel speed such as V₁-V₂ -V₁ . . . Following preferred embodiments will offer some systemsfor controlling this.

First Preferred Embodiment of a Control Apparatus

In a first preferred embodiment of the present invention, in addition tothe above basic construction, the molding machine control panel 17constituting a control apparatus of the extrusion molding apparatusaccording to the present invention has following construction as shownin a block diagram of FIG. 5.

The molding machine control panel 17 has speed data input means 25,difference factor calculating means 26, and operating means 27. Thespeed data input means 25 is to read speed instruction signals 21 forinstructing the above workpiece peripheral speed V, before molding.

The difference factor calculating means 26 is to input detected pressureP_(d) from the above pressure sensor 23, calculate material extrudingpressure P_(i) which is necessary at the above nozzle fore end 4 at eachvalue of workpiece peripheral speed V read by the above speed data inputmeans 25 by using a regression formula expressing the relation betweenthe above workpiece peripheral speed V and the above material extrudingpressure P, and obtain a nonlinear difference factor between the abovematerial extruding pressure P, and rotational speed N of the above motor10 on the base of the workpiece peripheral speed V stored in the abovespeed data input means 25, by comparing the calculated materialextruding pressure P_(i) and the above detected pressure P_(d).

The operating means 27 is to generate control signals 20 for controllingrotational speed N of the above motor 10 so that material extrudingpressure P at the above nozzle fore end 4 follows up changes in theabove workpiece peripheral speed V with the above nonlinear differencefactor taken as a parameter.

Next, the operation of the above construction will be described withreference to FIGS. 4 to 7.

As mentioned before, the workpiece 2 is traveled with respect to thenozzle fore end 4 at a high speed V₁ in the rectilinear travel sectionsL_(A), and at a low speed V₂ in the corner travel sections L_(B). FIG.4(A) shows the waveform of workpiece peripheral speed V in whichworkpiece peripheral speed V at the rectilinear portions is differentfrom workpiece peripheral speed V at the corner portions. This waveformof workpiece peripheral speed V is produced, for example, by usingsignals supplied from a speed sensor provided on a certain workpieceperipheral portion, or signals calculated from robot working speed V_(A)', V_(B).

Upon actuation of a start switch, the molding machine control panel 17executes Step S₁ for registering, in a certain memory, a regressionformula: V=f P! which expresses the relation between workpieceperipheral speed V and material extruding pressure P and which is usedin the processing of the difference factor calculating means 26.Concurrently with this, the robot control panel 14 executes Step S_(a)for setting a robot program in accordance with the shape of a workpiece(for example, working speed instruction v_(B) at the corner portions andv_(A) ' at the rectilinear portions, motion type instruction, etc.).

The regression formula: V=f P! has been obtained by conducting anexperiment to obtain the relation of workpiece peripheral speed V andmaterial extruding pressure P at the time when the cross sectional shapeof an extrusion material is maintained, and by specifying a functionwhich is most approximate to this characteristic by trial and error. Theobtained regression formula: V=f P! is expressed by almost straightline, as shown in FIG. 6. Therefore, the variation waveform of workpieceperipheral speed V and the variation waveform of material extrudingpressure P attain approximately similar figures in the case of idealmolding, as apparent from a comparison of the solid-line waveforms inFIGS. 4(A) and 4(B).

After the above preparatory processing, the molding machine controlpanel 17 and the robot control panel 14 start molding operation in StepS₂. When Step S₂ is carried out, the robot 11 holds a workpiece 2 by thearm 12 and allows a certain peripheral portion of the workpiece 2 to beengaged with the slit 4a of the nozzle fore end 4 of the extrusionmolding machine 15, whereby the robot 11 is ready to transfer theworkpiece 2. On the other hand, the extrusion molding machine 15 isready to discharge an extrusion material supplied in the hopper 16 fromthe nozzle fore end 4.

If the molding position immediately after molding starts lies in arectilinear portion of the workpiece 2, in Step S₃ a speed instructionsignal 21 from the robot control panel 14 is for instructing a highspeed V₁ and read by a certain register which constitutes speed datainput means 25. It is important that the speed instruction signal 21 forinstructing the high speed V₁ is read before the workpiece 2 istransferred (i.e., before molding starts). It is desirable that thetiming for advance reading is at least one program step before moldingstarts.

In Step S₄, the molding machine control panel 17 executes calculation bythe difference factor calculating means 26 by using the registeredregression formula: V=f P! to obtain a calculated material extrudingpressure P_(i), The calculated material extruding pressure P_(i) isnecessary material extruding pressure at the workpiece peripheral speedV₁.

Then, the molding machine control panel 17 executes a loop of Step S₅-Step S₆ -Step S₇ -Step S₈ -Step S₅ by the operating means 27: themolding machine control panel 17 inputs the detected pressure P_(d) fromthe material extruding pressure sensor 23 in Step S₅, calculatesdifference (P_(i) -P_(d)) between the calculated material extrudingpressure P_(i) and the detected pressure P_(d). determines thecalculation result in Step S₇, and when the difference (P_(i) -P_(d)) isa certain finite value (NO), the molding machine control panel 17 goesto Step S₈ to generate a control signal for instructing rotational speedN of the motor 10 which permits the material extruding pressure P at thenozzle fore end 4 to follow up a change in the workpiece peripheralspeed V. The operation of the operating means 27 in Step S₈ is generalPID control.

The operating means 27 which exercises the above PID control repeats theabove loop until the difference (P_(i) -P_(d)) converges onapproximately zero. During this, the rotational speed N of the motor 10is controlled and the material extruding pressure at the nozzle fore end4 becomes equal to the material extruding pressure determined by theregression formula, so that the extrusion material is discharged underthe material extruding pressure P_(i) which is necessary at theworkpiece peripheral speed V₁.

When the difference (P_(i) -P_(d)) is approximately zero, whether onecycle terminates or not is determined in Step S₉. In the middle ofmolding, the molding machine control panel 17 goes back to Step S₃ toread a speed instruction signal 21, and repeats the processing in andafter Step S₄ to calculate necessary pressure P_(i). That is to say, themolding machine control panel 17 exercises control for following up acommand workpiece travel speed V₂ in transferring from the rectilinearportion to a corner portion and control in transferring from the cornerportion to a rectilinear portion in a similar way.

In summary, in the above first preferred embodiment, the workpieceperipheral speed V at rectilinear portions attains a higher speed V₁than speed V₂ at corner portions. Accordingly, the robot can be operatedwith speed capability throughout the periphery of a workpiece, andthereby cycle time can be reduced.

In addition, the molding machine control panel 17 of the first preferredembodiment recognizes a change in workpiece peripheral speed V beforemolding, calculates material extruding pressure after the changebeforehand, and carries out advance control of the motor 10.Consequently, the nonlinear difference factor shown in the waveform ofmaterial extruding pressure (the dotted line waveform in FIG. 4(B) ) iscompensated, so that the respective characteristics of the workpieceperipheral speed V in a period T_(a) when it changes from the high speedV₁ to the low speed V₂, and in a period T_(b) when it changes from thelow speed V₂ to the high speed V₁ can be approximately in conformitywith the respective characteristics of material extruding pressure Pchanging from the high pressure P₁ to the low pressure P₂ and changingfrom the low pressure P₂ to the high pressure P₁, Thus, the firstembodiment can achieve molding with keeping the cross-sectional shape ofmoldings continuously.

Besides, because the regression formula: V=f P! can be a simple linearexpression, a coefficient can be most easily set with a slightmodification in view of disturbance.

Second Preferred Embodiment of the Control Apparatus

A second preferred embodiment of the present invention will be discussedwith reference to FIGS. 8 to 11.

As shown in FIG. 8, a control apparatus of the second preferredembodiment comprises speed data input means 25, basic data productionmeans 28, difference factor calculating means 29, and operating means30. The speed data input means 25 is to read peripheral speed of aworkpiece 2 with respect to the nozzle fore end 4 for one cycle, beforemolding. The basic data production means 28 is to produce basic data forgiving necessary rotational speed to the motor 10, from the travel speedstored in the speed data input means 25. The difference factorcalculating means 29 is to calculate a regression formula of a timedifference factor between changes in rotational speed of the above motor10 and changes in material extruding pressure, on the base of the travelspeed data read by the above speed data input means 25. The operatingmeans 30 is to correct the basic data produced by the above basic dataproduction means 28 along the time axis by the time differencecalculated from the above regression formula to produce final controlsignals.

The operation of the control apparatus of the second preferredembodiment is shown in FIG. 9.

In FIG. 9, Step S₁₁ to Step S₁₆ are preparatory processing beforemolding. Step S₁₁ is to register a regression formula: V=f ω! expressingthe relation between workpiece travel speed and rotational speed, i.e.,angular velocity of the motor 10. The regression formula is stored in acertain memory which is accessed by the basic data production means 28.

Steps S_(a) and S_(b) are carried out by the robot control panel 14. Itmust be noted that in Step S_(b) the robot control panel 17 operates therobot for one cycle while making the robot holding a workpiece 2.Accordingly, in the following Step S₁₂ a certain register reads theworkpiece peripheral speed for one cycle before molding, thereby servingas the speed data input means 25.

In this case, the workpiece peripheral speed V is stored as waveformdata shown in FIG. 10(A).

In Step S₁₃, the molding machine control panel 17 calculates respectiveangular velocities ω of the motor 10 which are required at time seriespoints t₁ to t₄ about the workpiece peripheral speed V by using theregression formula V=f ω! registered in Step S₁₁, thereby serving asbasic data production means 28. The respective angular velocities ω arebasic data on which control signals are based, and stored as a waveformwhich indicates continuous angular velocity variation. This basic datawaveform is shown by a broken line in FIG. 10(C).

In Step S₁₄, the waveform data of workpiece peripheral speed V read inStep S₁₂ are differentiated, so as to obtain workpiece speed changerates V' at the respective time series points t₁ to t₄.

In Step S₁₅, the molding machine control panel 17 calculates aregression formula S= V', V! expressing time difference s betweenchanges in rotational speed of the above motor 10 and changes inmaterial extruding pressure, with the workpiece peripheral speeds V andthe workpiece speed change rates at the above respective time seriespoints t₁ to t₄ taken as parameters, so as to obtain the variationwaveform (not shown) of time difference s at the respective time seriespoints t₁ to t₄, thereby serving as difference factor calculating means29.

This variation waveform of time difference s is calculated from thevalues of f V', V!, as shown in FIG. 11. f V', V! is expressed by apolynomial of V/V'. That is to say, each term (which will be a timefactor) obtained by dividing each workpiece peripheral speed V₁ in theneighborhood of, for example, a time series point t₁ by each workpiecespeed change rate V₁ ' at each time is totaled.

The neighborhood of a time series point t₁ is a period until theworkpiece speed change rate V₁ ' becomes constant. The respective timefactors s₁, s₂, etc. thus calculated express time constant in theinitial stage and in the final stage of a period when workpieceperipheral speed changes from one value to another value.

The molding machine control panel 17 applies this time constant tochanges in material extruding pressure, and at the same time convertsangular velocity of the motor 10 into time required for advance control.

In other words, when it is defined that the relation between workpiecetravel speed and angular velocity of the motor 10 is linear, and thatmaterial extruding pressure must follow up workpiece travel speed, it issupposed that the time lag s from a change in angular velocity of themotor 10 to a change in material extruding pressure is in proportion tothe time constant required for workpiece travel speed to change.

In the following Step S₁₆ the waveform data of angular velocity ωcalculated in Step S₁₃ are modulated by the characteristics of changesin the above difference factor S. That is to say, the waveform data aredisplaced along the time axis by the difference factor S at each of thetime series points t₁ to t₄ when workpiece peripheral speed changes.

As a result, the basic data are corrected as indicated by the solid-linewaveform in FIG. 10(C). The molding machine control panel 17 uses thesecorrected data as control signals for angular velocity of the motor 10in the following molding processes, thereby serving as operating means3.

After the above preparatory processing about one workpiece is finished,the molding machine control panel 17 goes to molding processing afterStep S₁₇ for the start of molding and repeats this molding processinghereinafter. That is to say, in Step S₁₈, the molding machine controlpanel 17 outputs the control signals obtained in Step S₁₆ for eachworkpiece and drives the motor 10, and in Step S₁₉ determines whetherthe molding of one workpiece is finished or not.

The control apparatus of the second preferred embodiment reads workpieceperipheral speed for one cycle, and when there is such a large timedifference between the change in rotational speed of the motor 10 andthe change in material extruding pressure as to prevent thecross-sectional shape of moldings from being maintained, the controlapparatus can produce control signals for compensating rotational speedin advance of this time difference.

The Third Preferred Embodiment of the Control Apparatus

A third preferred embodiment of the present invention will be discussedwith reference to FIGS. 12 to 16.

As shown in FIG. 12, the control apparatus of the third preferredembodiment comprises a pressure sensor 23, speed data input means 25,basic data production means 31, operating means 32, pressure waveformprocessing means 33, basic data correction means 34, and data switchingmeans 35. The pressure sensor 23 is provided to detect materialextruding pressure at the nozzle fore end 4. The speed data input means25 is to read beforehand travel speed of a workpiece for one cycle withrespect to the nozzle fore end 4. The basic data production means 31 isto obtain basic data from the travel speed data read by the speed datainput means 25. The operating means 32 is to operate the motor 10 forone cycle in cooperation with the robot 11, according to the basic data.The pressure waveform processing means 33 is to set time series pointswhen pressure change rate changes in the waveform of the detectedpressure P_(d) for one cycle output from the above pressure sensor 23.The basic data correction means 34 is to correct the basic data by timedifference between the time series point about the workpiece speedchange rate and the time series point about the above pressure changerate. The data switching means 35 is to store the data corrected by thebasic data correction means 34 in the above basic data production means31.

The control apparatus of the third preferred embodiment is operated asshown in FIG. 13.

In FIG. 13, Steps S₂₁ to S₂₅ (A) are preparatory processing beforemolding, and Steps S₂₆ to S₃₂ (B) are molding processing. Although inthe third preferred embodiment a neuronet type control is exercised inwhich data are corrected while molding processing is conducted, thiscontrol is basically the same as that of the second preferredembodiment.

In Step S₂₁, the molding machine control panel 17 registers a regressionformula ω=f V! shown in FIG. 14 and expressing the relation betweenangular velocity ω of the motor 10 and workpiece peripheral speed V.

Steps S₂₂ to S₂₄ are to serve as the speed data input means 25 and thebasic data production means 31. The molding machine control panel 17reads workpiece peripheral speed V by the robot 11 operated for onecycle in Step S_(b) (in Step 1), differentiates the read travel speeddata (the waveform shown in FIG. 15(A)) by time to produce the waveformof workpiece travel speed change rate V' shown in FIG. 15(B) (in Step2), determines an upper limit speed V₁ (rectilinear portion speed) and alower limit speed V₂ (corner portion speed) from the above travel speeddata (in Step 3), sets angular velocity ω₁ to ω₃ corresponding to theupper limit speed V₁, the lower limit speed V₂ and its average speed (V₁+V₂)/2 by using the above regression formula ω=f V! (in Step S₂₃), andconcurrently with Step S₂₃, sets time series points T₁ to T₃, T₄ to T₆when the workpiece speed change rate V' changes, from points ofintersection of each of a positive half cycle and a negative half cycleof the waveform of the above workpiece speed change rate V' andthreshold values ±a (a: an arbitrary constant) (in Step 4).

After these preparatory processing, in Step S₂₄ the molding machinecontrol panel 17 combines the above time series points T₁ to T₃, T₄ toT₆ with the data of the above angular velocity ω₁ to ω₃ and the angularvelocity change rates φ₁ to φ₃, and φ₄ to φ₆ (φ₃ and φ₆ are 0),

where

T₂ =(T₁ +T₃)/2

T₅ =(T₄ +T₆)/2

φ₁ =(T₂ -T₁)/(ω₂ -ω₁)

φ₂ =(T₃ -T₂)/(ω₃ -ω₂)

φ₃ =(T₅ -T₄)/(ω₂ -ω₃)

φ₄ =(T₆ -T₅)/(ω₁ -ω₂)

Thus set are instruction speed and instruction speed change rate for onecycle which are required by the motor 10.

The data set composed of angular velocity ω₁ to ω₃, and angular velocitychange rates φ₁ to φ₃, φ₄ to φ₆ is used for molding processing for thefirst cycle in Step S₂₅ to achieve molding of one workpiece.

Steps S₂₆,S₂₇ constitute pressure waveform processing means 33 which isa first step of molding of a second and other workpieces.

First, since detected pressure P_(d) from the pressure sensor 23 hasbeen input during the molding of the first workpiece, the waveform ofthe above detected pressure P_(d) (see FIG. 16(A)) is produced in StepS₂₆.

In the following Step S₂₇, the the waveform of pressure change rate P'is produced by differentiating the waveform of the detected pressureP_(d) by time (See FIG. 16(B)).

In Step S₂₈, in a similar way to the case with the angular velocity ω,time series points u₁ to u₃, u₄ to u₆ are set by setting thresholdvalues ±b (b: arbitrary constant) (see FIG. 16(B)).

These time series points u₁ to u₃, U₄ to u₆ (u_(n)) about the detectedmaterial extruding pressure Pd, and the time series points T₁ to T₃, T₄to T₆ (T_(n)), set in Step S₂₂, about the angular velocity ω, i.e.,rotational speed of the motor 10 according to the data set for moldingof the first workpiece respectively have time difference factors X₁ toX₆ (X_(n)). This relation is shown in FIG. 16(C). In FIG. 16(C), X₁ is atime difference between u₁ and T₁. X₂ is a time difference between u₂and T₂, . . .

In Step S₂₉, the molding machine control panel 17 corrects the timeseries points T_(n) by using the time difference T_(n) -u_(n), that isto say, calculates time difference X_(n) as advance time and thencorrects the time series points T_(n) into the time series points T_(n)-X_(n) thereby serving as basic data correction means 34.

In Step S₃₀, the molding machine control panel 17 combines the correctedtime series points T_(n) -X_(n) with corrected angular velocity changerates φ_(n) ', thereby serving as data switching means 35. The correctedangular velocity change rates φ_(n) ' are obtained by correcting angularvelocity change rates φ_(n) with the time difference X_(n) as follows.##EQU1## φ₂ '={2(T₃ -T₂)-(u₃ -u₁)}/(ω₃ -ω₂)

φ₃ '={2(T₅ -T₄)-(u₅ -u₄)}/(ω₂ -ω₃)

φ₄ '={2(T₆ -T₅)-(u₆ -u₅)}/(ω₁ -ω₂)

In Step S₃₁, molding is conducted according to the corrected data set.After molding, whether the molding is finished or not is determined inStep S₃₂, and when molding is finished with all workpieces, the programis finished.

In the above third preferred embodiment, because control signals arecorrected by automatically compensating data with the time differencefactor S during molding of each workpiece, the above third preferredembodiment has an advantage in that variations in the cross-sectionalshape of moldings can be reduced even when there are disturbance such aschange in temperature environment, and variations in resin materialcharacteristic values.

As a modification of the third preferred embodiment, it is possible toobtain time series points u_(n) about the pressure change rate by usinga regression formula expressing the relation between material extrudingpressure at the above nozzle fore end 4 and the above workpiece travelspeed, instead of using the pressure detected by the pressure detectingmeans 23 for one cycle.

This invention may also be applied to production of molded products byextruding a material on the surface of a workpiece and taking off amolded product from the workpiece after molding. The application of thepresent invention achieves molding with speed capability of a robot onboth the rectilinear portions and the corner curved portions ofmoldings.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed is:
 1. An extrusion molding apparatus comprising:anextrusion molding machine having a nozzle fore end and a molding machineactuator for delivering an extrusion material through the nozzle foreend to become a frame-shaped molding, the molding machine actuatorhaving an inoperative mode, an operative mode, and a working speed inthe operative mode; a robot for holding a workpiece on which saidframe-shaped molding is formed while imparting to said workpiece complexmotion including rectilinear motion and rotary motion, an operatingspeed of the robot being set to make travel speed of rectilinearportions of said workpiece relative to said nozzle fore end higher thantravel speed of corner portions of said workpiece relative to saidnozzle fore end; and a control apparatus comprising:speed data inputmeans for reading said workpiece travel speed relative to said nozzlefore end while said molding machine actuator is in the inoperative mode,and to provide a read workpiece travel speed; difference factorcalculating means for calculating at least one of a nonlinear differencefactor and a time difference factor between material extruding pressureand working speed of said molding machine actuator based on said readworkpiece travel speed, by using a regression formula expressing therelation of any two of said read workpiece travel speed, materialextruding pressure at said nozzle fore end, and the working speed ofsaid molding machine actuator; and operating means for controlling theworking speed of said molding machine actuator in the operative mode bycontrol signals generated to allow said material extruding pressure atsaid nozzle fore end to follow up changes in workpiece travel speed withsaid at least one of said nonlinear and time difference factors taken asa parameter.
 2. The extrusion molding apparatus according to claim 1,wherein the control apparatus further comprises:pressure detecting meansfor detecting material extruding pressure at said nozzle fore end whilethe molding machine actuator is in the operative mode; said differencefactor calculating means inputting detected pressure from said pressuredetecting means, calculating necessary material extruding pressure atsaid nozzle fore end at each value of said read workpiece travel speedby using the regression formula to express the relation between saidread workpiece travel speed and said material extruding pressure, andobtaining said nonlinear difference factor by comparing said calculatedmaterial extruding pressure with said detected pressure.
 3. An extrusionmolding apparatus comprising:an extrusion molding machine having anozzle fore end and a molding machine actuator for delivering throughthe nozzle fore end, an extrusion material to become a frame-shapedmolding, the molding machine actuator having an inoperative mode, anoperative mode, and a working speed in the operative mode; a robot forholding a workpiece on which said frame-shaped molding is formed whileimparting to said workpiece complex motion including rectilinear motionand rotary motion, an operating speed of the robot being set to maketravel speed of rectilinear portions of said workpiece relative to saidnozzle fore end higher than travel speed of corner portions of saidworkpiece relative to said nozzle fore end; and a control apparatuscomprising:pressure detecting means for detecting material extrudingpressure at said nozzle fore end; speed data input means for readingworkpiece travel speed for one cycle of workpiece travel relative tosaid nozzle fore end while said molding machine actuator is in theinoperative mode, and to provide a read workpiece travel speed; basicdata production means for differentiating a waveform of changes in saidread workpiece travel speed, setting time series points when saidworkpiece speed change rate changes, and setting instruction speed andinstruction speed change rate as control signals for the working speedto said molding machine actuator at each of said time series points;operating means for operating said molding machine actuator for anothercycle in said operative mode in cooperation with said robot based on adata set composed of instruction speed and instruction speed change ratefor the one cycle produced by said basic data production means at therespective time series points; pressure waveform processing means forcalculating pressure change rate from the wave form of detected pressurefor the another cycle output from said pressure detecting means andsetting time series points when said pressure change rate changes; basicdata correction means for calculating time difference between the timeseries points of said workpiece speed change rate and the time seriespoints of said pressure change rate, and correcting said data set bysaid time difference; and data switching means for storing said data setcorrected by said basic data correction means in said basic dataproduction means as said control signals in order to conduct molding fora next cycle.
 4. In an extrusion molding apparatus comprising:anextrusion molding machine having a nozzle fore end and a molding machineactuator for delivering an extrusion material through said nozzle foreend to become a frame-shaped molding, the molding machine actuatorhaving an inoperative mode, an operative mode, and a working speed inthe operative mode; a robot for holding a workpiece on which saidframe-shaped molding is formed while imparting to said workpiece complexmotion including rectilinear motion and rotary motion, an operatingspeed of the robot being set to make travel speed of rectilinearportions of said workpiece relative to said nozzle fore end higher thantravel speed of corner portions of said workpiece relative to saidnozzle fore end; and a control apparatus comprising:speed data inputmeans for reading workpiece travel speed for one cycle of workpiecetravel relative to said nozzle fore end while said molding machineactuator is in the inoperative mode, and to provide a read workpiecetravel speed; basic data production means for producing basic data fordeveloping said working speed of said molding machine actuator at eachvalue of read workpiece travel speed by using a regression formulaexpressing the relation between said read workpiece travel speed andsaid working speed; difference factor calculating means for calculatinga workpiece travel speed change rate by differentiating the waveform ofchanges in the read workpiece travel speed for said one cycle ofworkpiece travel, and for calculating a time difference factor between achange in said working speed of said molding machine actuator and achange in material extruding pressure at said nozzle fore end, using theregression formula with said workpiece travel speed and said workpiecespeed change rate taken as parameters; and operating means forcorrecting said basic data produced by said basic data production meansalong a time axis with said time difference factor calculated by saidregression formula and producing a control signal.